Traction type elevators are known as elevator drive systems.
In these systems, a machine room is installed above the elevator in which a traction machine is equipped, a car is suspended on one end of a rope, and a counterweight is suspended on the other end of the rope.
However, since the traction machine is relatively large and a brake system of the elevator, control unit and so on are also to be found in the machine room, the machine room requires a large area. In an apartment building, in which a residence space is required to be large as possible, the area occupying the machine room becomes an even greater problem. In addition, the weight of the system in the machine room requires that the structure of the machine room be cost effective, in terms of rigidity.
To solve the above-described problems, an elevator system in which a linear motor is the driving source has been developed. Since the linear motor is a machine whose motor itself makes a linear motion instead of a rotating motion, traction sheaves and so on are not required as they are as in a traction machine and a light-weight elevator system can be achieved. Therefore, since no machine room used for the traction machine installed for the elevator is required, a reduction in size of the whole elevator system becomes possible. In this way, major features in the linear motor driven elevator systems are provided.
Three phase power cables are connected between a linear motor moving element, installed in a counterweight suspended opposite to a car, and an inverter installed in a machine room not above the car. In these cables, a multiple number of copper wires coated with vinyl for each phase are bundled radially in cross section and covered with an insulating material, e.g., polyvinyl chloride. Since the power cables are suspended and spatially moved with the movement of the linear motor (and counterweight) and are used for a long duration of time, such movement could create problems of wear. Copper wires in the individual power cables tend to become bent, folded, and broken and, in worst cases, mutual copper wires are contacted so that a short circuit occurs. Further, if one or more strands of the copper wire is broken in any one of the power cables, current flowing through the other copper wires is increased and a heat is generated in the corresponding power cable. Consequently, the power cable becomes deteriorated and the function of the power cable becomes lost or diminished.